Kennels often use cages having at least two compartments, one located inside the building offering protection from bad weather and the other located outside the building offering access to fresh air and sunshine during good weather. A kennel door typically separates the two compartments and serves to permit the animal to move freely between them, while at the same time protecting the inside of the building from the weather and insects found outside. Predictably, the kennel environment imposes special requirements on such doors which are different, in degree and in kind, from the requirements imposed on doors used by humans. For example, an animal must be able to easily operate the door to both enter and exit the building without human assistance. After each time the animal has passed through the door, the door must automatically and effectively close and protect the interior space from the outside conditions. In addition, the door must be capable of withstanding unusual and considerable abuse without breaking. In the past, however, kennel doors have not satisfactorily met all these requirements.
Kennel doors have characteristically been of two types: doors which are hinged at the top and doors which are hinged on one side. Both of these designs have shortcomings. They are prone to flying open in a stiff wind unless provided with a strong hinge-spring, a magnet or other mechanism to hold them closed. These mechanisms, however, are not altogether satisfactory solutions to the problem. The hinge-spring, which is a torsional spring oriented along the axis of the hinge, discourages the animal, particularly puppies and small dogs, from using the door by making the door more difficult to open. Moreover, because the hinge-spring is part of the hinge, shielding it from the moisture and corrosive conditions typically present in the kennel is very difficult. Thus, it tends to corrode quickly and fail. When it fails, it generally cannot be repaired using commonly available components; but rather, the entire hinge and hinge-spring assembly must be replaced. As a consequence, not only is its repair an annoyance, it is unnecessarily expensive.
Magnets, on the other hand, do not discourage animals from using the door, however, they are not particularly reliable. After repeated use, the magnets become misaligned and no longer hold the door shut as intended.
Another shortcoming exists in designs using a single door which swings both ways to allow the animal to both come and go. In such doors, there is by necessity a small gap around the door which allows in unwanted drafts, rain and insects. Some designs have solved this problem by using two doors, an inner door mounted within an outer door. The outer door has a lip on one side which acts as a seal and permits the door to swing only in one direction; whereas, the inner door has a lip on the opposite side which also acts as a seal but permits that door to swing only in the opposite direction. Thus, for example, the animal exists by pushing the outer door open and enters by pushing the inner door open. Obviously, these designs have twice as many moving parts as the single door designs and are more complicated. Thus, they present greater opportunity for failing and prove to be less durable.